the timing of the use of this weapon was simply the appropriate tactical moment against the proper target to use this particular munition. it s not related to any outside events. reporter: it does deliver a psychological message to isis. one military official tells cnn the massive bomb is powerful enough to destroy nine city blocks. it will level that area and provide an unbelievable amount of concussion to that area. so it will collapse caves, blow up things and it will if you re alive afterwards, you re going to have perforated eardrums and a lot of drama. reporter: general nicholson says it all went as planned. caves and tunnels destroyed and dozens of isis fighters killed. we have persistence surveillance over the area before, during and after the operation and now we have afghan and u.s. forces on the site and see no evidence of civilian